A thermoelectric module (TEM) contains a number of alternating p-type and n-type semicondcutor thermoelements (e.g., n and p diodes) serially connected and disposed between two thermally conducting, but electrically insulating substrates. When an electric current is passed through the TEM, heat is absorbed at one face (one of the substrates) and rejected at the other face. The TEM thus functions as a cooler or refrigerator. A TEM may be used as a thermoelectric cooler in applications where small size, high reliability low power consumption and a wide operating temperature range are required.
FIG. 1 illustrates a typical TEM in accordance with the prior art. TEM 100, shown in FIG. 1 includes multiple n and p diode pairs 110, which are typically electrically connected in series with conductive connecting strips 115. Typically the space 111 between diode pairs 110 contains air. The diodes are disposed between two substrates 120A and 120B. Typically such substrates are formed by bonding several (e.g., three) ceramic layers together. When a current is connected through the negative terminal 125A and the positive terminal 125B, one side of the TEM (e.g., substrate 120A) will absorb heat, and the other side (e.g., substrate 120B) rejects heat. The side of the TEM that absorbs heat is referred to as the “cold side” and the side of the TEM that rejects heat is referred to as the hot side. Which side of the TEM is the cold side and which the hot side is determined by the polarity of the current. That is, reversing the current changes the direction of the heat transfer.
FIG. 1A illustrates a side view of the TEM 100.
TEMs can be used to cool a heat generating component by attaching a heat generating component to the cold side of the TEM and applying a current. TEMs can likewise be used to heat by reversing the TEM physically or reversing the current.
When used to cool a heat generating component, the TEM will not function efficiently unless a heat removal device is attached to the hot side. This is because the TEM is designed to maintain a specified temperature difference, ΔT, between the cold side of the TEM and the hot side of the TEM. As heat from the heat generating component is absorbed by the cold side, the hot side gets increasingly hot in order to maintain the temperature difference ΔT. The hot side of the TEM can get so hot that the TEM fails.
To address this situation, a heat removal device (e.g., a heat sink) is attached to the hot side. Typically, a thermal interface material (TIM) is used to reduce the contact resistance between the heat removal device, which may be a copper or aluminum block with fins, and the TEM substrate. The TIM fills the voids and grooves created by the imperfect surface finish of the two surfaces. Such voids and grooves can be highly thermally resistant. The TIMs used, typically polymers or grease, are thermally conductive materials. Even with the use of TIMs, the thermal resistance at the TEM/heat removal device interface can be excessive and detrimental for some applications.